This invention relates generally to the dispensing of materials from pressure vessels and, more particularly, to pressure vessels which, when punctured, dispense liquids and foams from the puncture site and to methods of filling such vessels. In an important embodiment, this invention relates to security systems for impeding unauthorized ingress to or egress from a secure space by delivering an entry retardant from a puncture site of a pressure vessel along the perimeter of the secure space or into tunnel-like entrances into such secure spaces.
There are many applications in which it is desirable to dispense a liquid or foam from a pressure vessel by simply puncturing the vessel wall to dispense the liquid or foam from the puncture site. For example, as described below, such vessels could be used in an activated barrier to protect sabotage and theft targets by dispensing a liquid or foam to impede ingress or egress across the barrier if it is breached. In fact, such vessels could be used in any application in which it is desirable to be able to reliably dispense a liquid or foam from a randomly chosen location on the vessel wall. For example, in addition to security applications of the type already mentioned, such vessels could be used to dispense materials for smothering or containing fires in response to any shrapnel or heat producing event such as the explosion of a bomb, the disintegration of a piece of machinery, or the disassembly of a nuclear reactor core.
Pressure vessels of the general type described must include an ullage containing a cover gas under pressure to force the material in the vessel through the puncture site. Unfortunately, in horizontal applications of prior art vessels, puncture of the vessels at the ullage will release the gas and thereby depressurize the system without delivering the material in the vessel. In security and many other potential applications for such vessels, this risk of disarming the system by puncturing the vessel at its ullage is not acceptable and the prior art vessels are therefore little used in such applications.
The current techniques for protecting various secure spaces, such as atomic energy facilities, embassies, military research and intelligence facilities from unauthorized ingress and egress of persons and objects include enclosing such spaces with concrete, hardened steel plate, or other passive barriers. Unfortunately such passive barriers are often inadequate to prevent or significantly delay penetration by sophisticated, well armed intruders. Thus there is a considerable need for a system, to be used either alone or in conjunction with such passive barriers, which can be activated either by force or on command to provide a higher level of protection.
One such activated system which has been suggested for delaying breach of secure spaces by intruders and thereby aiding in their capture is set forth in U.S. Pat. No. 4,202,279. This patent describes a sticky foam material in a low boiling point solvent which is maintained under pressure in its liquid form and delivered into the secure space from a single pressure vessel when there is an unauthorized attempt to gain entry by penetrating past the vessel. The resulting breach of the vessel releases the liquid foam material from the solvent to spew out of the vessel as a greatly expanded sticky foam adhering to the floor of the secure space and to the tools and the intruder attempting to use them in a "tar baby" fashion making it extremely difficult to use the tools or to walk or crawl over the foam and into or out of the secure space.
It has also been suggested to create an extended barrier by interconnecting a number of pressurized vessels containing sticky foam liquid in a low boiling point solvent as described in the above U.S. Pat. No. 4,202,279. In FIG. 1 there is illustrated such an assemblage 2 of four pressurized tanks 4A-4D each comprising a tube 6 with welded hemispherical end caps 8 and 9 and an axial, internally threaded opening in each end cap (not shown). The tanks are interconnected at the bottom openings in caps 8 through threaded couplings 10A-10D, to a lower common tubular manifold 12 which is closed off by a threaded plug 14 at one end and by a ball valve 16 coupled to the other end. Threaded couplings 18A-18D fitted to the axial openings in the top end caps 9 of the tanks interconnect the tanks to check valves 20A-20D leading to another series of threaded couplings 22A-22D and a top common tubular manifold 24. Manifold 24 has a threaded plug 26, ball valves 28 and 30 and a pressure gauge 32 coupled to valve 30.
The device of FIG. 1 is filled by first introducing an inert cover gas such as nitrogen through valve 28 and valves 20A-20D into each of the tanks, 4A-4D, while the system is maintained in a vertical position. Manifold 12 permits the pressure in tanks 4A-4D to equalize. Once the minimum pressure necessary to maintain the sticky foam in an unexpanded liquid state is obtained, typically about 100 psi., the liquid is introduced through valve 16 and manifold 12. Sufficient liquid is used to fill the tanks to a desirable level, say 80% by volume, driving the nitrogen pressure to the vicinity of 400 psi. This leaves an ullage containing roughly 400 psi nitrogen gas in the upper 20% of each tank so long as the system is maintained in a vertical position.
This prior art system has many significant drawbacks. It is expensive since it requires at least one valve for each cylinder and manifold and numerous couplings and other hardware. Its reliability is questionable and its life expectancy is short since its numerous threaded pipe connections are all potential sites for leakage. The high pressure produced on filling the system further increases the likelihood of failure at the fittings and elsewhere in the system.
In addition to the expense and questionable reliability of the system of pressurized tanks illustrated in FIG. 1, this system suffers from other even more serious drawbacks. Once a system of the type illustrated in FIG. 1 is filled, it must be transported and used in a vertical position. If the system is tilted significantly from the vertical position, the ullages at the tops of tanks 4A-4D could be shifted around in the system to an unbalanced configuration, such as that illustrated in FIG. 1A, where the sticky foam is designated at 34 and the ullage is designated at 36. Restoration of the initial distribution of the ullages in this prior art system would be extremely difficult, if not impossible.
In the unbalanced configuration of FIG. 1A, a puncture of cylinder 4D at point 38 would release all of the cover gas in the system without ejecting any sticky foam liquid. In fact a puncture of any of the other cylinders would result in release of the cover gas after ejecting only the sticky foam liquid between the puncture and the ullage in tank 4D leaving the remainder of the system unemptied. Furthermore, the prior art system depicted in FIG. 1 can be effectively used only in a vertical position. This is a serious drawback, for example, in security applications where it is necessary to protect horizontal floors and ceilings of a secure space.
Yet another problem with the prior art system of FIG. 1 is that it is extremely difficult to mount since both manifolds and each tank 4A-4D must be firmly supported in order to prevent a break at the manifold connections. This problem becomes acute when it is desired to mount the system in a movable member such as a door.